The Quad 303 power amplifier is intended for normal domestic use with loudspeakers of moderate efficiency, but is also used by broadcasting and recording studios, groups and discotheques world wide, who appreciate its excellent performance and dependability.
The outstanding performance of the Quad 303 is largely due to the unique output circuit developed by Quad.
The Quad 303 is normally used with the Quad control unit, but can readily accommodate other signal sources. Since it has no controls it can be mounted out of sight in a well ventilated cabinet.
The amplifier won a Council of Industrial Design Award in 1969
The circuit employs symmetrical triples, greatly reducing distortion and rendering the quiescent current independent of output transistor temperature.
This development enables the designers to reduce distortion to any desired degree without sacrificing stability, and to maintain this excellence under all dynamic conditions.
To put this in perspective, the lowest theoretical distortion present on the very best tape and disc will still be some hundred times greater than that of the Quad 303.
Such a level is, of course, completaly inaudible no matter how refined the test.
The use of triples, permits simple and effective control of the output current and since the voltage is also controlled, the output transistors are completely protected and must always operate within their ratings with the obvious advantages of greatly improved reliability under all conditions, without the use of elaborate and expensive circuitry.
The amplifier cannot be upset even when overdriven by an asymmetrical signal or by shorting or disconnecting the loudspeakers.
The chassis and covers of the Quad equipment are in die cast aluminium and sheet steel finished in stove-enamelled
metallic beige and brown with off-white and marigold push buttons and control panels. The control unit, top left, and
the tuner, lower left, can be positioned together or separately. The amplifier, above, has no controls, and can
therefore be housed out of sight in a cabinet or cupboard, heat dissipation being greatly assisted by the aluminium
fins at the rear.
The amplifier is intended for use with loudspeakers of 4 - 16 Ω nominal impedance.
Poweroutput and distortion for various frequencies.
Continuos sine wave into 8Ω resistive load.
100 Hz any level up to 45 watts<0.03% Dtot
1 kHz any level up to 45 watts <0.03% Dtot
10 kHz any level up to 45 watts <0.1% Dtot
Output Internal Impedance: 0.3Ω in series with 2000μF and 6μF
Frequency Response: Ref. 1 kHz -1dB at 30 Hz and 35 kHz into 8Ω
Signal Input Level: 0.5V rms ±0.5 dB for 45 watts into 8Ω.
Amplifier loads the input by 22kΩ in parallel with 60 pF
Signal Input Overload: Instantaneous recovery up to +20 dB overload.
Crosstalk (input loaded by 1 kΩ): 30 Hz - 10 kHz > 60 dB
Hum and Noise (input loaded by 1 kΩ): "A" weighted -100 dB ref full power. Unweighted (15.7 kHz measurement bandwidth) -95 dB ref full power
Protection: This amplifier is suitable for use under the most arduous music conditions with speakers of impedances between 4 and 25Ω and for high level sine wave duty with loads of 8Ω or greater.
Stability: Unconditionally stable with any load
Power Input: 100-125 or 200-250 V, 50/60 Hz, 40-200 watts depending on signal level.
Dimensions: 120 x 159 x 324 mm (W x H x D)
Weight: 8,2 kg